Abstract
This study was undertaken to evaluate the effects of the supine posture, immersion,
and swimming on hormones involved in the regulation of hydrosaline equilibrium. Plasma
levels of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), plasma renin
activity (PRA), and aldosterone (ALDO) were measured by radioimmunoassay in eight
untrained young subjects (five males and three females). Blood samples were collected
on different days: control morning samples in a relaxed standing posture before each
test; after 20 min in a supine position; after 20 min of horizontal immersion in water
at 28 °C; after 20 min of backstroke swimming (speed about 1 m/s). No changes occurred
in AVP levels after each test. ALDO and PRA increased significantly only after swimming
and were directly correlated. ANP increased significantly after immersion, but no
further increase was observed after swimming. The hematocrit, which increased after
swimming, was inversely correlated with ANP levels in the post-exercise samples. These
data show that while ALDO and PRA increase only in response to swimming, even at moderate
intensity, ANP probably requires more prolonged and intense exercise to reach a significantly
higher level than in immersion.
Key words
atrial natriuretic peptide - renin - aldosterone - arginine vasopressin - supine posture
- immersion - swimming
